A process of this kind for steering a motor vehicle is known from DE-OS 36 36 533, which pertains to a four-wheel steering system for a motor vehicle. In the known four-wheel steering system, the front wheels are turned in the usual way by means of a steering wheel actuated by the driver, which acts on a front wheel steering gear. A mechanical transfer device transfers the steering motion to a coupling drive which acts on a rear wheel steering gear in order to turn the rear wheels, with the coupling drive defining the steering angle ratio, namely, the ratio between rear wheel steering angle and front wheel steering angle.
In this case, the coupling drive can be adjusted, as a function of the vehicle speed, in such a way as to cause the rear wheels to turn in the opposite direction at low vehicle speeds and to cause the rear wheels to turn in the same direction at high vehicle speeds, with the steering angle ratio being set, when the rear wheels are both the opposite-direction and same-direction turning ranges, as a function of the vehicle speed.
In addition, the paper entitled "Four Wheel Steering System with Rear Wheel Steering Angle Controlled as a Function of Steering Wheel", S. Sano et al, SAE Technical Paper Series 860625, 1986, discloses a process for controlling a four-wheel steering system for a motor vehicle, in which the steering angle ratio is set as a function of the steering angle of the front wheels by means of a corresponding gear arrangement. In this case, advantage is taken of the fact that in normal driving, large front wheel steering angles essentially occur only at low vehicle speeds, while small front wheel steering angles essentially occur at relatively high vehicle speeds. Therefore, in this known process for controlling a four-wheel steering system, the steering angle ratio and therefore the rear wheel steering angle are also, to an approximation, set as a function of the vehicle speed.
In four-wheel steering systems controlled according to these known processes, the rear wheels of the motor vehicle also turn even at very small front wheel steering angles. At driving speeds above a predefined speed or at small front wheel steering angles, the rear wheels are turned in the same direction as the front wheels, while at driving speeds below the predefined speed or at large front wheel steering angles, the rear wheels turn in the same direction. As a result, the driving and steering characteristics of the vehicle are altered over the entire speed range.
In normal driving, when only low values of the transverse acceleration and yawing moment are reached, an additional rear wheel steering system to reduce these values is not only unnecessary by also disadvantageous, since the fact that the rear wheels turn in the same direction enhances the understeer characteristics of the vehicle and reduces steering responsiveness.